Vatican City
The city within a city! We visited the city on the last Sunday of the month (i think... cannot really remember the exact date lol) and it was free entrance for all. We were expecting a super long queue, but were still surprised by the number of tourists in line. The line stretched almost three quarters around the city, and later we heard that those that were half way in the line didn't even make it. We made the right choice of not joining the queue but went for the Basilica St Pietro instead. 
From ground level, we climbed up a long series of spiralling steps until we hit the basilica itself, where we climbed up further (in between the dome. The dome is a double shell. Incredible isn't it!?) and got a wonderful view of the entire city. It was so crowded!
